Field of the Invention
This invention relates in general to the enlargement of earth duct around a semi-rigid pipe in which the pipe has previously been buried and surrounded by the earth. The invention is particularly described with respect to what is known as 4 inch schedule 35 polyvinyl chloride (pvc) pipe but is not restricted thereto.
The problem addressed and which this invention solves is how to remove or reduce the surrounding inward pressure of the earth material exerted towards the outside surface of a given buried pipe, (such as a 4" schedule 35 vertical sanitary vent which has been lifted out of its T fitting trap by frost), so as to thereby enable enlarging the diameter of the earth duct tunnel surrounding same. Such pvc vertical sanitary vent pipes have been installed in thousands of home lots in northern parts of the United States; and within a time span, of such as short as one year or a few years after installation, upward pressure exerted upon such pipes by the repeated freezing and thawing of the ground near its surface causes the pipes to heave and become separated from the T-fitting traps to which they are originally connected, thereby leading to environmental and pollution problems, as are referred to in more detail hereinafter.
In the past, choices made to solve said problems have been to excavate from the surface to remove the surrounding ground pressure to allow removal or adjustment of this pipe; or to try to force the pipe downward to return it into the T-lifts trap below, but typically misalignment of the pipe in relation to the T-fitting trap generally inhibits re-insertion because of slight sideward displacement (as well as vertical displacement) of the pipe. Also, deeper sewer lines create more friction from the earth to inhibit press reinsertion without pipe damage.
The shortcomings of such alternatives are the harm done to the appearance of the ground surface and also the time delay between total ground settlement and finish grading to restore the ground surface to its "pre-excavation" state, and appearance, as well as high relative expenses as compared to the method of this invention. And reinsertion only temporarily solves the problem, for the frost action continues.